I wondered that, too. It seems that one of the ways in which language changes is the gradual creep of slang/informal usages into what is considered to be correct. Another one that really jumps out at me is 'busted' to mean broken. This was definitely considered improper back in my school days...

"The fiery general, in charge of the military component of the mission, lost his rag during a press conference..."

Where did THIS phrase come from?

Apparently the word "rag" is an old British slang reference to the tongue, also called the "red rag". (No, don't go there). To "chew the rag" is to talk, and to "lose one's rag" is to lose control of one's tongue.